Product and process



Oct. 28, 1969 M.

D. ZEl-SBERG PRODUCT AND PROCESS Filed June 29, 196'? FIG INVENTORMILLARD D. ZEISBERG ATTORNEY United States Patent O 3,474,616 PRODUCTAND PROCESS Millard David Zeisberg, Newark, Del., assignor to E. I.

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware Filed June 29, 1967, Ser. No. 649,944 Int. Cl.D02g 3/36'; D01d 11/06; B44d 1/22 U.S. Cl. 57-164 7 Claims ABSTRACT FTHE DISCLOSURE Plexiflamentary strand material is impregnated uniformlywith particulate material. A rod-shaped batt of longitudinally collapsedplexifilamentary strand material is mounted so that a cone of the strandmaterial pulled from one end of the batt is at least partially submergedin a suspension of the particulate material. The strand material ispulled continuously from the end of the batt through the suspension.

Background This invention relates to the impregnation of continuousplexilamentary strands with particulate materials and to the compositestructures so prepared.

Numerous products are known which combine particulate materials withcontinuous strands of tow, yarn, or roving. These include, for example:sized textile yarns, such as cotton strands sized with starch;electrical conductors formed by impregnating or coating rayon fiberswith graphite or conductive carbon; strands comprising short-fiberasbestos formed from dispersions of the short fibers with a variety ofadditives (see, for example, Wilke et al. U.S. Patent No. 2,972,221);further strands cornprising short-fiber asbestos comb-ined with longerstrands of cotton, rayon, or nylon or with continuous metallic wires;fiber-reinforced strands combining fibrous material with cementitiousmaterials (see British patent specification 1,042,606); strands produceddirectly from slurries of Wood pulp and then woven into sheets orwrapped around wires for insulation; and any number of compositestructures resulting from drawing strands through mixtures ofparticulate solids with binders to coat and/or impregnate the strands.

When a iiexible strand or roving is to be combined with other materials,it has been necessary to employ low viscosity solutions or dispersionsin order to promote penetration of impregnant to the core of the strand.Viscous agents or large-particle suspensions invariably coat or encasethe strands rather than uniformly impregnate the strand material. Theformation of composite flexible strands using non-fibrous particles,i.e., particles of globular, spherical, Hake, or plate-like shape, hasbeen dilcult and ordinarily produecs composite strands in which thecontinuous iibrous material and/ or added binder constitute a largeproportion by weight.

Certain particulate materials have been intractable because of size,shape, or intrinsic nature, and frequently no feasible or economicalmethod is available to form strands of these particles in a :supportingmatrix to provide the desired characteristics. Often the very presenceof a binder, or the large quantity of binder required to hold theparticulate materials together, interferes with obtaining desiredphysical characteristics, eg., flexibility, conformability, porosity,and absorptivity.

3,474,616 PatentedOct. 28, 1969 comprising a three-dimensional integralplexus of syn-k thetic organic polymeric, fibrous elements having thestructural conguration of film-fibrils which exhibit a thickness of lessthan about 4 microns and which are so nely divided as to impart to thestrand a total surface area of at least 2 m.2/gm. Preferredplexifilamentary strands are those disclosed in Blades and White U.S.Patent No. 3,081,519, issued Mar. 19, 1963.

The rod-shaped batt disclosed in the Belgian patent is characterized inthat, from either end, or from new ends formed by breaking the batt atany point along its length, a single continuous plexifilamentary strandcan readily be pulled. The strand comes oi the batt as an integral,generally circular, open network which collapses radially to a yarn-likestrand at a point downstream. Thus, the strand assumes a cone-shapedconfiguration as it is pulled from the end of the batt, with the apex ofthe cone pointed in the direction of strand travel.

Summary of the invention According to this invention there is provided acornposite structure comprising solid particulate material uniformlydistributed throughout a plexilamentary strand. The invention alsoprovides a method for producing such a structure which comprises thesteps of (l) providing a suspension of solid particulate material in adispersing medium, (2) mounting a rod-shaped batt of longitudinallycollapsed continuous plexitilamentary strand material such that a coneof plexilamentary strand material pulled from one end of said batt is atleast partially immersed in said suspension, and (3) continuouslypulling said plexilamentary strand from said batt through saidsuspension.

Brief description of the drawings FIGURE 1 is a partly sectional drawingillustrating one embodiment of this invention wherein a rod-shapedplexilamentary batt is immersed in a suspension of particulate materialand an end of plexiiilamentary strand is continuously withdrawn while atleast a portion of its cone remains submerged.

FIGURE 2 is a representation of a plexiilamentary batt suitable for useaccording to this invention.

FIGURE 3 is an enlarged view along the opened length of a plexilamentarystrand impregnated throughout with particulate material.

FIGURE 4 illustrates in partial cross-section an alternative method forimpregnation according to this invention wherein the batt is mountedoutside of the suspension of particulate material.

FIGURE 5 is analogous to FIGURE 3, showing preferential alignment ofacieular particles generally parallel to the longitudinal axis of theplexilamentary strand.

FIGURE 6 is a schematic drawing of an overall equipment arrangementpermitting continuous coupled operation according to this invention.

Description of the preferred embodiments With reference now t-o FIGURE2, a suitable plexilamentary batt 1 is discussed in more detail. Thecrosssectional shape of batt 1 is circular, but oval, polygonal, andother cross-sectional shapes are equally suitable. These cross-sectionalshapes can be solid or hollow, the latter resultingeitherif'thei'plexitilament is` Vcollected in an' ari` nular space or ifthe solid batt is later hollowed by axial boring. A single continuousplexilamentary strand 2 can be withdrawn from either end of batt 1. Abatt 1, or any section broken from it, ordinarily has a convex end and aconcave end 4, convex end 5 being the one first formed and concave end 4the one from which continuous plexilamentary strand 2 is prefera-blywithdrawn. In collecting a plexiilamentary strand in the form of batt 1,the strand balloons so that the multitudinous interconnected lilmibrilelements constituting the strand at any point'are deposited `throughoutan enlarged generally circular area, which area should be at leastone-fourth and preferably at least `two-thirds of the area of concaveend 4 of batt 1. Subsequent pulling of the plexilamentary strand 2 froman end of batt 1 generates a generally conical section 3 ofplexiilament, cone 3 having an apex away from the end of battwl alongthe withdrawal direction and a base at the end of batt 1 correspondingto the generally circular area of previous deposition. Plexilamentarystrands with deniers from to 100,000 or greater can be collected asbatts and subsequenty pulled from them. The batt 1 ordinarily has alength of from 1/5 t0 1/3000, preferably 1/1000 to l/gooo, of the lengthof plexiiilamentary strand 2 which can be pulled from it; and thedensity of suitable batts 1 is generally between about 16 and 240kg./m.3, preferably between about 110 and 135 kg./m.3.

One embodiment of the process of this invention is now discussed withreference to FIGURE 1. A suspension of particulate material 8 indispersing medium 6 is provided in a suitable contaner 12. Aplexlamentary batt 1 is submerged in the suspension, and a continuousplexiiilamentary strand 2 is continuously pulled from end 4 of batt 1through and away from the suspension. As discussed hereinabove,withdrawing the strand 2 creates a cone 3 of plexiiilamentary material,and it is critical to this improved strand-impregnation process that atleast a portion of cone 3 be immersed below the upper level 7 of thesuspension. As indicated in FIGURE l, particulate material 8 iswithdrawn substantially unformly dispersed within strand 2.

FIGURE 3 is an enlarged representation of an impregnated plexilamentarystrand 2, the strand having been opened by lateral tensioning to renderit substantially planar and to reveal the internal distribution ofparticles 8. The iineness of the multitudinous interconnectedfilmfibrils 9 forming the plexus of strand 2 results in so extenr sivecontact with the particles 8 that the composite structure isunexpectedly coherent and durable without the use of binders. Forexample, a dry composite strand containing ZO'parts by weight of woodour per part of linear polyethylene film-fibrils loses as little as 6%by weight of the wood our after a one-foot (30.5 cm.) long strand isvigorously shaken twice.

Another embodiment of the Yprocess of this invention is depictedschematically in FIGURE 4. A suitable container 12 is provided withasuspension of particulate materialV 8 in a dispersing medium 6. Batt 1is mounted generally outsd'e the suspension so that, whenplexifilamentary strand 2 is pulled downward from its face 4, cone 3 isat least partially immersed-below level 7 of the suspension. A guideIQll or rod 17 within the suspension translates Vthe forceofstrandremoval into a downward force at face 4 of "batt 1. As in FIGUREl, strand 2 leaves the suspension with particles 8 intimatelydistributed throughout. The amount of particles thus incorporatedgenerally increases as more of cone 3 is immersed, and maximumimpregnation results when the level of suspension is raised to thatshown by dotted line 10 corresponding to immersion of face 4 of batt 1.

FIGURE 6 represents schematically an overall coupled process forpreparing a finished strand, any or all of the auxiliary functions ofwhich -may be used as desired. If twist is to be imparted to the iinalstrand, it is conveniently obtained by mounting batt 1 in a holder 16which can rotate'asV indicated by arr`ow I9. In' order to maintain'level 7 of the suspension and to replenish particulate material 8removed with strand 2, means for continuously introducing freshsuspension are required, such as indicated lby side-tube 18. Ordinarilythe concentration of particles 8 in fresh suspension is greater thanthat maintained in vessel 12. By providing, for instance, a set offriction-rolls 20 and a set of draw-rolls 22, stretch-elongation isimparted to strand 2 in the region 21 therebetween. A drying region 24,for instance an over 23 supplied with heated gases at 25, may also beprovided. Finally,rthe finished strand is either wound-up into asuitable package 26 or 'drawn on to other alternative processing steps.

Particulate material useful in this invention can be substantially anyfinely divided (i.e., volume less than about 1, cubic millimeter),dispersible solids with any particle shape, e.g., spherical, globular,Hake, plate-like, acicular, or iibrous. Examples of suitable particulatematerials include wood flour, asbestos shorts, potassium titanate,diatomaceous earth, nylon flock, lead powder, aluminum flake, acicularboron nitride, activated charcoal, conductive car-bon, and the like.Suitable suspensions can be mechanically maintained or colloidallydispersed or a suspending agent can be used.

Liquid dispersing mediums are ordinarily employed. Water is the mostcommon dispersing medium, but many other liquids, such as alkanols andhalogenated alkanes, form suitable suspensions, as are well-known in theart. The dispersing medium can also be gaseous, e.g., uidized beds ofthe particulate materials. As is readily apparent, numerous otheradditives can be dissolved or suspended in the dispersing medium, theseadditives including, for example, wetting agents, binders, dyes,buffering agents, and the like.

The film-fibrils constituting a plexilamentary strand have lapredominantly longitudinal orientation, as is evidenced by much greaterresistance to tearing by longitudinally than by transversely appliedforces. The introduction of acicular particles according to the processof this invention also results in their being predominantlylongitudinally oriented, which effect is enhanced by subsequentlydrawing the impregnated strand. FIGURE 5 shows the longitudinalorientation of acicular particles 11 in a strand 2, laterally opened asin FIGURE 3.

The following examples are representative of the breadth of applicationof this invention. In them, all ratios and percentages are by weightunless specifically indicated otherwise. The batt used in most of theexamples is a 4.84 crn. diameter batt of plexifilamentary linearpolyethylene as described in Example I of the aforesaid Belgian PatentNo. 670,293. Diifering sizes, shapes, and polymeric compositions of battare indicated where applicable, this particular one being designatedsimply as a 4.84 cm. diameter polyethylene batt. While linearpolyethylene is the preferred polymer, anypolymer which can formplexiiilaments and which can be collected as a v'batt according toBelgian Patent No. 670,293 is suitable.

EXAMPLE I A 4.84 cm. diameter polyethylene batt is impregnated withminus 300 mesh wood flour (Eastern White Pine or Douglas Fir) by theprocess of this invention. Except for the lack of continuous drying, theapparatus and procedure employed are as shown in FIGURE 6. Thesuspension employed is composed of 2.55 gm. of wood flour, 100 cc. ofwater containing 1% of isooctyl phenyl polyethoxy ethanol wetting agent,and 3.14 gm. (based on solids) of aqueous dispersion of ethyl acrylatepolymer particles of less than 0.5 micron size. The batt is mounted inthe holder but is not rotated. With its cone immersed in the suspension,the polyethylene plexilament is withdrawn at about 6.8 meters/min. :andis drawn (region 21 of cessive 1.27 meter lengths and dried. Approximateirnpregnation equilibrium is reached after about 20 samples areobtained, characterization of samples 27, 29, 3l and 33 being given inTable I.

TABLE I.-CHARACTERIZATION OF IMP RE GNATED STRANDS WOOD-FLOUR StrandBreaking Residual Diameter Strength Elongation Sample No Denier (rum (kgPercent Due to the presence of acrylic binder, the bulky strand is freeof dusting. The weight of dry Wood flour retained is lbetween 6.5 and7.5 times the weight of the original plexiilamentary strand. The strandsare useful as iiller cords for conductive cables.

EXAMPLE II A 4.84 cm. diameter polyethylene batt is used for preparing astrand impregnated with medium length asbestos ber. Apparatus andprocedure are in accordance with FIGURE 6. The asbestos shorts(predominantly crocidolite) exhibit the following size distribution in aRO-Tap 30-minute, 100-gm. analysis:

A suspension is prepared from 20() gm. of these aS- bestos shorts, 30cc. of a sodium silicate solution, and 40 cc. of non-ionic isooctylphenyl polyethoxy ethanol in 8 liters of water. The water-solution ofsodium silicate has a specific gravity at 60 F. (15.5 C.) of 50.25 B.and contains 28.50% S102 and 15.00% Na2O.

Polyethylene plexiiilamentary strand is withdrawn from the batt throughthe suspension at 12.5 meters/min. while the batt is rotated at 550r.p.m. Subsequently the impregnated strand is drawn 17.5% and dried. A2.54 meter long sample is taken for every 7.5 to 10.0 meter length ofdried strand, with results shown in Table 1I.

TABLE IL CHARACTERIZATION OF ASBESTOS-FIBER IMP RE GNATED ST RAND S DryWeight Percent .Asbestos Sample No. (gm.l meters) Polyethylene Cut Afabric woven from wood-Hour impregnated polyethylene plexiiilament isdescribed.

The suspension employed for impregnation is composed of 300 gm. of theWood flour of Example I, 100

cc. of a resin emulsion, 8 liters of water, and 40 ce. of nonionicisooctyl phenyl polyethoxy ethanol wetting agent. The resin emulsion(Velsicol Chemical Corp. Stikvel P-65, said to be a cyclopentadienederivative) is a tacky, non-drying, non-oxidizing emulsion containing65% of solids which are less than 1 micron in diameter.

Impregnation is according to FIGURE 6. 'Ihe 4.84 cm. diameterpolyethylene batt is rotated at 1000 r.p.m.; strand is withdrawn at 27.5meters/min.; a 22% stretch is imposed; and the impregnated strand isdried. It is characterized as follows:

Average weight-2.52 gm./ 10 meters Breaking strength-1.14 kg. ResidualElongation-26.7%

A portion of the strand is woven into a conventional piamweave fabricwith 4.73 Warp-yarns and 6.50 fill-yarns per centimeter. The 1.42 mm.thick fabric weighs 276 gm./m.2. It is smooth in appearance and isremarkably drapeable and soft for this thickness making it a highlydesirable yet inexpensive fabric for decorative use such as in draperyand tapestry. Specific gravity of the fabric is only about 0.2.

EXAMPLE IV A suspension of line acicular potassium titanate particles informed by intensively mixing 30 gm. of the particles in 500 cc. ofwater. The volume is increased to 1350 cc. with water, and 150 cc. of10% isooctyl phenyl polyethoxy ethanol wetting agent is added.

A 4.84 cm. diameter polyethylene batt is immersed in the suspension asshown in FIGURE 1, and impregnated strand is withdrawn without twistingat about 20 meters/ min. Samples 1.27 meters long are taken throughoutthe run and dried. Results are shown in Table yI'II.

TABLE IIL-POTASSIUM TITANATE IMP RE GNATED POLY ETHYLENE STRANDS DryWeight Percent Sample No. (gm./10 m.) Polyethylene The suspension is notreplenished during this operation. From the almost linear decrease instrand weight with time (sample number), at least after the fourthsample is taken, it is apparent that solids level in the remainingsuspension is decreasing and that the plexus of strand material passingthrough the suspension preferentially concentrates the acicularparticles within it.

EXAMPLE V A lter-cartridge prepared from impregnated strands of thisinvention is described. A 4.84 cm. diameter polyethylene batt isprocessed as shown in FIGURE 6 with zero twist. Strand is withdrawn at25.5 meters/min., stretched 17%, and oven-dried to constant Weight atbelow C. (about 13 C. below the melting point of the linearpolyethylene). The suspension employed is composed of 1200 gm. of afilter aid, 8 liters of water, and 200 cc. of 10% isooctyl phenylpolyethoxy ethanol wetting agent. The ilter aid is nely divideddiatomaceous earth of which 92% has particle sizes less than 40 microns,79% less than 20 microns, 46% less than 10 microns, and none less than 2microns. The ratio of wet to dry strand weights is about 4.35; andrepresentative 50 cm. lengths of dry strand weigh from 10 to 11 gm./ 10m. after processing into -lter cartridges.

To produce the cartridge ilter, the dried strand is iirst transferredfrom its collection spool onto a 5.08 cm. diaemter cardboard tube andthen pulled over the end onto 25.4 cm. of the length of a 30 cm. long,2.54 cm. diameter perforated core. The windup pattern used is known asan 8-traverse pattern in which 8 separate diamond crossover pointsprogress around the outer circumference in a plane at right angles tothe long axis of the perforated core. Final diameter of the completedcartridge is 4.25 cm.

The cartridge filter exhibits a pressure drop of 20.8 cm. of mercury forair flow through it of 84 liters/min. Filtration etliciency is testedusing an aqueous suspension of carbon black of a particle sizecharacterized as 0% greater than 18 microns, 25% greater than 10ymicrons, and 50% greater than 5 microns. Solids at a concentration of-20 parts per million are fed to the filter at 2.3 grams per hour for 11hours (final pressure drop is 182 crn. of mercury). Final liltrationefciency is 88%, and averaged overall efiiciency is about 80%. After 6%of the total time, particulate rseidue in the eiiiuent is less than 2parts per million.

EXAMPLE VI Using a 4.84 cm. diameter polyethylene batt and apparatus asshown in FIGURE 6, three more wood-Hour impregnated strands are madeusing diifering concentrations both of the 30G-mesh wood iiour and ofthe added binder.

The binder employed is a high molecular weight, hot water-solublepolyvinyl alcohol which, in 4% solution at C., exhibits a viscosity bythe Hoeppler falling ball method of between 55 and 65 centipoises.Strand withdrawal rate for each case is 15.3 meters/min.

In each of the three cases, the suspension comprises 2 liters of water,20 cc. of isooctyl phenyl polyethoxy ethanol, X cc. of a 10% aqueoussolution of the polyvinyl alcohol, and Y gm. of the wood our.

Case No. X Y

TABLE IV.-PROPERTIES OF THREE WO OD-FLO U R/POLY- ETHYLENE STRANDSBreaking Residual Twist Strength Elongation Case No. Denier (turns/cm.)(kg.) Percent EXAMPLE VII An impregnated strand comprising cut nylon ockand plexiiilamentary linear polyethylene is described.

The suspension is formed from 1 gram of cut nylon ock and one liter ofwater containing 1% of isooctyl phenyl polyethoxy ethanol. The flock isprepared Iby cutting 3 to 5 denier nylon lament into random lengthsbetween 0.5 and 2 mm., the predominant length being about 0.75 mm.

A 4.84 cm. diameter polyethylene batt is immersed in the suspension asshown in FIGURE 1. Successive lengths are prepared by manuallywithdrawing about l meterV of strand, adding twist of about 0.5turns/cm., and cold stretching by about 10%. After several samples arewithdrawn, examination of subsequent samples with a 5- power magnifyingglass shows preferential longitudinal alignment of the ilock within thecomposite strand.

EXAMPLE VIII Fabric of asbestos impregnated yarn according to thisinventon is compared with an analogous 4fabric: containing conventionalasbestos yarn.

The anthophyllite asbestos shorts selected are known to have excellentresistance to acid, alkali, and heat but to exhibit poor spinnabilityand poor iiexibility. Dry screen analysis (U.S. Sieve Series) shows 46%of the shorts to be less than 65-rnesh and 0% larger than 6-mesh.

A suspension is prepared from 500 gm. of asbestos shorts, 8 liters ofwater containing 1% of isooctyl phenyl polyethoxy ethanol, and 75 cc. ofthe sodium silicate solution of Example II. A 4.84 cm. diameterpolyethylene batt of about 800 denier plexilament is impregnatedaccording to FIGURE 6, strand withdrawal rate being 38 meters/min. androtation of batt-holder 16 being at 1000 r.p.m. The dried impregnatedstrand contains between 10 and 15% polyethylene and weighs from 4.6 to5.4 gm./ 10 meters. This strand corresponds to an 8 to 10 cutcornmercial yarn.

A plain-weave fabric from the strand of this example has 4.54 warp and6.30 ll yarns/cm., weighs about 382 gtn./m.2, and is 1.42 mm. thick. Thefabric is soft and smooth and possesses unusually soft conformability.To the contrary, an analogous fabric woven from 10-cut commercialasbestos yarn as till shows the usual fuzziness and is so stiff that itcannot drape or conform readily.

Pressed for l5 minutes under 315 l g./crn.2 pressure between platensheated to C., the fabric of this example becomes stiif and looks wet.Subsequent unrestrained heating for 2 minutes in a 200 C. oven causes noshrinkage, and the cooled product shows good strength retention.

EXAMPLE IX impregnated strands comprising the diatomaceous earth ofExample V and linear polyethylene plexilarnents are prepared accordingto a statistical design of variables and used to construct miniiilters.The operating conditions which vary are shown in Columns 2-5 of Table V.In each case a 4.84 cm. diameter polyethylene batt is impregnatedaccording to FIGURE 6 at a constant wind-up rate for the product of 7.65m./min. Each suspension is composed of the weigth of diatomaceous earthshown in Column 2, the volume of emulsion binder shown in Column 3, and2 liters of water containing 1% of iso! octyl phenyl polyethoxy ethanol.The binder emulsion contains 45i0.5% of a polyvinyl chloride copolymerof 0.1 to 0.2 micron particle size. The batt is rotated at the rateshown in Column 4, and the stretch indicated in Column 5 is imposed onthe impregnated strand. Each dried product is transferred from itscollection reel onto a conventional textile 30 paper cone, and thepercentage loss in weight by dusting of diatomaceous earth during thisstep is given in Column 6.

Minilters are constructed from each strand. They are formed on 1.91 cm.diameter, 17.15 cm. long perforated tubes, each perforation being 3.18mm. in diameter and triangularly spaced from others on 6.35 mm. centers.Each end of each tube is masked with vinyl tape to leave perforationsexposed along 9.53 cm. of length, and the tube is wound with 52 helicaltraverses along its central 14.6 cm. of length. The Weight of the strandused, in gm./ 10 meters, is shown in Column 7; and filter porosity aspressure drop in crn. of water for air-flow at 14 liters/ min. is givenin Column 8.

TABLE V Mini-Filter Porosity cm. Diato- Imposed Weight Loss Strand H2Ofor 14 maceous Emulsion Rotation, Stretch, in coming, Weight, litersSample N o. Earth, gms. Binder, ce. r.p.m. percent percent gms/10 m.air/min Examination of these results shows that the dusting loss ofColumn 6 decreases markedly at lower levels of imposed stretch. Pressuredrop for constant air-ow also decreases (i.e., porosity increases) withdecreasing imposed stretch. For lower twist levels, porosity decreasesat higher levels of binder; but the reverse is true at the high levelsof twist. Dusting loss increases for increased twist at low levels ofbinder, but is insensitive to twist at high binder levels. The amount ofimpregnation by the diatomaceous earth is primarily a function of itsconcentration in the slurry, particularly at lower levels of binder.Decreased imposed stretch decreases the amount of impregnation.

EXAMPLE X TABLE VI.-BATTS OF DIFFERING SIZES AND SHAPES Plexiflla-Impregnated End- Plexilament Strand Dimensions ment, Weight Weight BattShape (cm.) Denier (gm/10 m.) (gm./1O m.)

Rectangular. 2. 7 x 2. 35 479 0. 43 10. 8 D 4. 4 X 5. 5 666 0.60 12. 1Cy1indrical 2. 35 180 0. 16 3. 9 D0 4. 84 967 0.87 27. 5

The 4.84 cm. diameter batt is unexplainably more eicient than theothers, but an almost linear relationship between impregnated strandweight and relaxed denier of the plexiiilament exists for the otherfour.

EXAMPLE XI Impregnation of plexilamentary polyethylene with lead isdescribed. A suspension of minus-300 mesh (U.S. Sieve Series) leadpowder is prepared from 378 gm. of lead and 100 ce. of a 1% solution ofnon-ionic wetting agent in water. A 2 cm. long piece of 4.84 cm.diameter polyethylene batt is immersed in the suspension as shown inFIGURE l, and the suspension is continuously agitated in its 250 ml.beaker using a rotary magnetic stirrer. An approximately 50 cm. longlength of impregnated strand is manually withdrawn.

An exceedingly high pick-up of lead is attained. The wet strand weighs1100 gm./ l0 meters, decreasing to 990 gm./ 10 meters on drying. Theweight of dry strand is 1135 times greater than that of unimpregnatedplexifilament, and the dry strand contains less than 0.1% linearlpolyethylene by weight.

The impregnated strand is also unusually cohesive and is, in fact, asoft rod about 6.5 mm. in diameter. A Section of this product is fed tothe nip between two solid metal 5.1 cm. diameter rolls rotating at about20 r.p.m. The product emerging is a ribbon of plexilament-reinforcedlead about 12.7 cm. wide and from 0.28 to 0.46 mm. thick. Theplexilament apparently assists in drawing the strand into the nip of therolls.

EXAMPLE XII A suspension is prepared from 50 gm. of aluminum flake, 2liters of Water containing 20 cc. of isooctyl phenyl polyethoxy ethanol,and 10 cc. of the binder emulsion of Example IX. The aluminum iiake ischemically pure aluminum of the type added as pigment to paint.

Operating in accordance with FIGURE 6, a 4.84 cm. diameter polyethylenebatt is mounted in holder 16 and and is rotated at from 320 to 345r.p.m. Wind-up of impregnated strand is at 7.65 meters/min., Sample Areceiving 9 to 10% imposed stretch, and sample B 40%.

An electrical charge decay test at 21.1 C. and 65% relative humidity(Rothchild charge decay) is performed by clamping specimens across the2.54 cm. gap between to conductive clamps, imposing a voltage, andmeasuring the decay of imposed charge as a function of time. Sample A,weighing 1.25 gm./ 10 meters, decays as follows: 31.8% in 0.5 min.;52.7% in 1.0 min.; 74.9% in 2 min.; and in l0 min. Sample B, weighing2.8 gm./l0 meters, decays much more rapidly: 99.2% in 0.5 min.; 99.8% in1 min.; and 100% in 2 min. Both samples are conductive for staticelectricity. An unimpregnated plexiiilamentary polyethylene strand showsessentially no charge decay over extended periods of time. The compositestrands of this example can be incorporated in minor amounts in fabricsof conventional yam to prevent static build-up.

EXAMPLE XIII A 0.3 gm. spongy mass of acicular boron nitride issuspended in 300 cc. of water by high-speed mixing. Volume of thesuspension is then doubled by addition of a 1% aqeuous solution ofnon-ionic wetting agent. A 4.84 cm. diameter polyethylene batt istreated as shown in FIGURE 6 except that no replenishment of suspensionis provided. A twist of about 1 turn/ cm. is applied, strand iswithdrawn at 2 to 3 m./min., and 26% stretch is imposed before drying.

The weight gain by impregnation is so low that it cannot be computed bymeasuring the weight of impregnated strand. By dissolving thepolyethylene in perchloroethylene, the initial product is shown tocontain 3.96% solids, and a later product 1.29%.

Opaqueness of the plexilamentary strand makes direct observation oflongitudinal orientation of the acicular particles substantiallyimpossible. One technique for detecting alignment is to press theimpregnated strand to a lm between heated platens and then to examinethe film at Z50-diameter magnication under a circroscope. Delinitelongitudinal orientation of agglomerates of boron nitride particles isobserved. It is observed that strands impregnated with boron nitrideexhibit much less shrinkage and distortion on being pressed to a lm thando unimpregnated plexilaments. Stereocan photomicrographs of theuncompressed strands at magnications up to 3000 also reveal agglomeratesof boron nitride needles with a denitely preferred orientation along thestrand axis. The strands can be used in place of conventional boronnitride strands as fillers in plastics.

EXAMPLE XIV Using the procedure of Example XII, with an activatedcharcoal suspension rather than lead particles, another impregnatedstrand is obtained. The suspension is prepared from 50 gm. of activatedcharcoal and one liter of water containing 1% each of non-ionic wettingagent and the polyvinyl alcohol of Example VII.

yAfter the manually withdrawn strand dries in air, its weight is 41 gm./10 meters at a diameter of 6 to 7 mm. Only 2.1% of the weight of theimpregnated strand is polyethylene. It is almost free of dusting and isreadily wettable by water. A fabric is woven from the composite strandmaterial of this example to provide a convenient form for use infume-absorption applications. lIt results that the 1% isooctyl phenylpolyethoxy ethanol added to the suspension as non-ionic wetting agentdeactivates the activated charcoal with respect to fumeabsorption.Another fabric prepared identically except that of butanol is used assubstitute wetting agent performs excellently in fume-absorptionapplications.

EXAMPLE XV This example described the preparation of sponge yarnsaccording to the method of this invention. In each of three cases, a4.84 cm. diameter polyethylene batt is mounted as shown in FIGURE 1 anda strand is manually withdrawn.

In the irst case, the suspension contains 13.5% cellulose and iscomposed of 70 gm. of viscose, 340 gm. of nely divided Glaubers salt, 43gm. of water, and a trace of pink pigment. After cellulose regeneration,removal of Glaubers salt, and drying, the resultant sponge yarn weighsabout 7 gm./10 meters. Its water absorbency is 13A-fold by weight, andunder mild linger pressure it wrings out to only 31.2% of its weight.The cellulose sponge is uniformly reinforced by the plexilamentarystrand matrix.

In the second case, the suspension is composed of 70 gm. of viscose, 340gm. of nely divided Glaubers salt, 100 gm. of water, 0.2 gm. of isooctylphenyl polyethoxy ethanol wetting agent, and ya trace of pink pigment.Presence of wetting agent in this case increases the cross-sectionalarea of the impregnated strand by 6 to 8 times.

The third sample is prepared as in the second case except that theimpregnated strand is sized by being drawn through the stem of alaboratory funnel to decrease its cross-sectional area to substantiallythat obtained in the iirst case.

The sponge yarns of this example can be used to make sponge mops. Theyarns are superior to sponge yarns presently used for this purpose sincethe sponge is reinforced throughout its three dimensions by theplexiiilamentary strand. Y

While these examples illustrated a great breadth of application of thisprocess of preparing impregnated strands based on the plexifilamentarybatts disclosed in Belgian Patents No. 670,293, they by no means exhaustthe possibilities.

toY

12 crystalline particles of barium, lead, and strontium ferrites which,as disclosed in U.S. Patent No. 3,113,927, are exposed to a magneticlield before being sintered. Similar results can be expected frompractice of this invention if the suspension is exposed to a magneticfield during strand-impregnation.

It is Well-known to prepare yarnsor fibers of intractable materials suchas polytetrauoroethylene or graphite using auxiliary carrier materials.The normally Weak yarns are subsequently rendered coherent by, forexample, fusion, sintering, or pyrolysis. Similar structures can beprepared using plexiiilaments from batts as carriers.

In still another application, plexiilamentary strands are impregnatedwith diminutive seeds, such as tobacco or petunia seeds, to facilitatetheir handling and even distribution. They can simultaneously beimpregnated with chemical agents, such as fungicides and fertilizers,topromote germination. Many other applications for metering particulatesolids are immediately evident.

Still further, impregnated strands comprising drying agents, such asalumina and silica gel, or ion-exchange resins can be converted tofabrics for constructing belts or loops which can be mechanically andcontinuously moved through a unit where their function is employed andthrough a second unit where their function is regenerated.

It is known to encapsulate uids, such as perfumes, medications, andcleaning agents, in wax, gelatin, or other microscopic hollow spheres.These fluids become active by rupture of their spheres in use. Theimpregnation of plexilamentary strands with such dry fluids provides aconvenient way to dispense and use them.

Finally, plexilaments impregnated with a brous base Aand/or lubricantscan serve excellently as packing materials in pumps, valves, and thelike.

EXAMPLE XVI A completely unexpected advantage of this invention is thatthe weight gains by impregnation as described herein are far greaterthan attained by any known method. This example provides comparison datain support of this observation. Table VII lists the pertinent data. Inall cases, impregnation is accomplished as indicated in FIGURE 1. Twoloose cotton rovings (one weighing 2.88 gm./l0 meters with 1 turn per2.54 cm., and the other weighing 3.00 gm./ 10 meters with 4 turns per2.54 cm.) are compared with the use of a 4.84 cm. diameter linearpolyethylene batt from which a plexiiilamentary strand weighing only0.86 gm./ 10 meters can be pulled. In Table VII, pairs of cotton-rovingresults are shown, the result at lower twist above that for highertwist. In each case, the suspension has the concentration of particulatematerial given in Columns l and 2. The dispersing medium is watercontaining about 1% of the isooctyl phenyl polyethoxy ethanol wettingagent.

From examination of Columns 3 and 4 it is immediately obvious that thelow-weight plexilament picks up far more particulate material than doesthe cotton roving. Columns 5 and 6 present the ratio of weights of dryimpregnated strand and of unimpregnated base strand. For theplexilament, these ratios are seen to be at least an order of magnitudehigher than for cotton roving. In every instance, moreover, the cottonroving is found to be more coated than impregnated, while theplexilamentary material is found to be uniformly impregnated throughout.

Over most of the concentration range for particulate material, theweight gain by impregnation increases substantially linearly withconcentration, but, as is evident from Table VII, the highestconcentrations are proportionately less efficient. This indicatesr theexistence of a limiting concentration for practical and economicalimpregnation above which the suspensions become too As an example,permanent magnets are produced from viscous to penetrate the strandssuiiiciently rapidly. It is 13 apparent that the highest concentrationslisted in Table VII are near the limiting concentrations.

TABLE VIL-COMPARISON IMPREGNATION OF COTTON ROVINGS AND POLYETHYLENEPLEXIFILAMENT Pickup Ratio Dry Strand (Dry Weight] Weightt(gx1./10Inigiali Sltxnd me ers e g Concentration Plexi- Plexi- (gm./ Cottonfila- Cotton lila- Partieulate Material 100 ce.) roving ment rovingment,v

5. 55 1. 95 Diatomaceous Earth 5 ,1 08 20 1 38 23.3 1o ggg 39 45.3 2o18o gigi 209 -25 8 5 iso 209 wood muur 2.5 l 3U 3o 1; 47 34.9 5 59 68.67.5 g: 99 j} 115 7. 95 2. 8 *1o l Q zml 11s 3 14} 137 *N ear maximumconcentrations.

Furthermore, impregnation of plexifilaments according to this inventionhas a completely unexpected concentrating effect with respect to thedispersed particulate materials. This is evidenced in three separateobservations.

First, with increasing concentration of particulate material in thesuspension, the ratio of wet to dried Weight of impregnated stranddecreases, i.e., the wet strand retains a noticeably higher relativeproportion of solids. Thus, the wet/dry weight ratios for the strands ofTable VII are, in order: 6, 4.5, 3.1, and 2.5 for diatomaceous earth;and 5.35, 5.35, 5.0, and 4.5 for wood our.

Secondly, regardless of particle concentration, the weight of dry strandcomputed from the weight of wet strand and from the knownsuspension-concentration is always less than the measured dry weight.This indicates that the particles are preferentially removed from thesuspension, a fact which could be applied, for instance, to the removalof solid wastes from efiiuent streams. For example, with reference toTable VII for the suspension containing diatomaceous earth at 5 gm./ 100cc., the wet weight of the strand produced is 118 gm./ 10 meters.Subtracting the 0.86 gm./l meters weight of plexifilament yields aweight pick-up of 117.14 gm./l0 meters which, if it has the sameparticle concentration as the suspension (4.76 gm. of solid per 100 gm.of suspension), should contribute 5.58 gm. of dry particles to the 10-meter strand. The measured dry weight is, however, 20.0 minus 0.86 gm./10 meters, indicating that 3.43 times as much impregnation by solidparticles is attained over the amount expected. Similar calculations forthe 2.5 and 5.0 gm./100 cc. concentrations of wood fiour yield ratios of7.50 and 3.83 respectively.

Lastly, as shown in several examples, the concentration of particulatematerial in suspensions unreplenished by fresh suspension decreases withcontinued impregnation, which also shows preferential removal of theparticles.

As illustrated in the examples, the ratio of the weight of particulatematerial to the plexifilamentary material in the composite strand canvary widely, depending upon the specific gravity of the particulatematerial, its concentration in the suspension, the size and shape of theparticles, etc. Thus, the weight of the particulate material may be aslittle as 0.01 times the weight of the plexus or even less, or it may beas great as 1500 times the weight of the plexus or even greater. Asindicated previously a particular advantage of the process of thisinvention is that the weight gains are far greater than attained byknown impregnation methods. Thus it is in preparing composite yarnswherein the Weight of the particulate material is several fold (e.g., to1000 fold) the weight of the plexifilamentary material that the processoffers its most significant advantage.

It is not completely understood why the process of this invention is sounexpectedly efiicient in impregnating the plexiiilamentary strand withparticulate solids. At least a portion of the explanation seems,however, to depend on the cone (3 in the figures) of plexifilamentaryplexus which forms as strand is drawn from a batt. Thus, as a tinyvolume of plexitlament at the end of a batt is pulled out into an openplexus, it suddenly generates a much greater new volume which, when thecone is at least partially immersed in suspension, creates a pumpingeffect moving suspension into the strand. The results indicate theexistence of at least two processes. First, suspension in large volumeis pumped into the expanded plexus. Secondly, while the plexuscollapses, a portion of suspension must be squeezed back out withselective filtration of particles by the condensing plexifilament. Thus,there is enhanced accumulation of particles within the strand. Thisconcentration by filtration is apparently more eliicient for lowersuspension concentrations. Whatever the explanation, it is clear thatimpregnation according to this invention is dilerent in kind from andsuperior to known impregnation and coating ope-rations.

A pair of companion impregnations tends to confirm both the pumping andthe filtration effects of the collapsing plexus. Two portions of a 4.84cm. diameter polyethylene batt are separately impregnated Whilecompletely immersed (as in FIGURE 1) in a 3% suspension of asbestosshorts. One portion is first bored out to provide a 0.5 inch (1.27 cm.)diameter hole axially along its whole length. The hollow portion picksup about 54 gm. of asbestos per 1000 inches (25.4 meters) ofstrandlength 4while the solid portion picks up only about 41 gm. This isconsistent with the hypotheses that a pumping effect draws freshsuspension through the hollow center and that the concentration ofsuspension reaching the center is greater than results if the suspensionis all filtered in through the plexus of fibrils in the cone.

Numerous uses for this invention are disclosed in the foregoing examplesand specifications. Many other uses and applications of the inventionwill be readily apparent to those skilled in the art.

I claim:

1. A process for making a composite strand comprising solid particulatematerial uniformly distributed throughout a three-dimensional integralplexus of synthetic organic polymeric lm-fibril elements whichcomprises:

y(a) providing a suspension of solid, particulate material in adispersing medium;

(b) mounting a rod-shaped batt of longitudinally collapsed continuousplexifilamentary strand material such that a cone of plexifilamentarystrand material pulled from one end of said batt is at least partiallyimmersed in said suspension; and

(c) continuously pulling said plexifilarnentary strand from said battthrough said suspension.

2. A process as defined in claim 1 wherein said rods'haped 'batt iscontinuously rotated to impart twist to the strand.

3. A process as defined in claim 1 wherein said cone is substantiallycompletely immersed in said suspension.

4. A process as defined in claim 1 wherein stretchelongation is impartedto said strand after impregnation by said suspension.

5. A process as defined in claim 1 wherein said suspension iscontinuously replenished to maintain a substantially constantconcentration of particulate material.

l6. A process as defined in claim 1 wherein said rodshaped batt isaxially bored.

7. A process as defined in claim 1 wherein said suspension includes abinder.

(References on following page)

